1. Field of the Invention
The present invention relates generally to light weight inflatable structures and the like. The present invention relates more specifically to structural members in the nature of air beams that may be utilized in group assemblies or arrays to configure a large inflatable structure, especially for the construction of light weight inflatable buildings and the like.
2. Description of the Related Art
There have been many efforts in the past to utilize inflatable elements in the construction of portable, light weight buildings, enclosures and the like. There are many benefits to be gained through the use of such light weight enclosures, including the ability to easily transport and quickly erect the structures. Transportability depends upon the structure being flexible, foldable, compact and light weight when in a deflated condition. Rapid set-up (inflation) depends upon limiting the volume of air that must be injected into the structure to provide sufficient size, shape and support.
Some efforts to provide light weight inflatable structures have focused on pressurizing the interior of the entire enclosure as with an inflated dome roof. This approach has a number of drawbacks that include the need for a base framework to hold and seal the edge of the structure to the ground or other surface on which the structure is erected. Perhaps the primary drawback to this approach is the need to provide a means for entry into and exit from the interior of the enclosure while maintaining the necessary inflation pressure. Typically this means maintaining an air pressure source that may constantly and automatically replenish the air within the enclosure.
More recent efforts to create inflatable structures have focused on utilizing closed xe2x80x9cair beamxe2x80x9d elements that, when inflated, provide a more or less fixed structural element. These air beams are typically tubular in cross section and are constructed of air impermeable fabrics. Often these air beams are shaped to establish the configuration of the enclosure upon inflation, such as with arch shaped tubes, each end of which may be fixed to the ground. An array of such tubes may be connected and joined with flat fabric elements that provide the wall and/or roof enclosure for the overall structure. Examples of some of these efforts include the following:
U.S. Pat. No. 6,108,980 issued to Braun on Aug. 29, 2000 entitled BUILDING ELEMENT, describes a structural design for light weight buildings and the like having cellular wall elements with alternating positive and negative pressure chambers. The objective of the positive and negative pressure chambers is to draw components of the structure together in a manner that restricts their movement with respect to each other.
U.S. Pat. No. 4,288,947 issued to Huang on Sep. 15, 1981 entitled MODULAR INFLATABLE DOME STRUCTURE, describes a modular dome structure that includes a number of rigid frame members in addition to the inflatable dome surface. Specialized Y-joints for connecting the rigid frame members are described. All inflatable members are designed to harden after inflation by vulcanization and curing.
U.S. Pat. No. 5,311,706 issued to Sallee on May 17, 1994 entitled INFLATABLE TRUSS FRAME, describes an inflatable truss frame according to a variety of different geometric embodiments. In each instance, the truss structure is defined by the specific geometry of the individual inflatable sections and the manner in which these components are themselves formed from Mylar sheeting and the like.
U.S. Pat. No. 5,677,023 issued to Brown on Oct. 14, 1997 entitled REINFORCED FABRIC INFLATABLE TUBE, describes an inflatable tube for use as a structural element that incorporates spiraling, high strength ribbons mounted on a fabric skin surrounding an inflatable bladder. Reinforcing ribbons are also positioned on the outside of the skin parallel to the axis of the tube to strengthen the tube against bending forces.
U.S. Pat. No. 5,735,083 issued to Brown et al. on Apr. 7, 1998 entitled BRAIDED AIRBEAM STRUCTURE, describes an air beam that includes a cylindrical external braid that is lined with an air impermeable bladder. The improved design described is resistant to buckling because of linear bundles of fibers that extend parallel to the axis of the cylindrical braid and within the cylindrical weave.
U.S. Pat. No. 4,146,996 issued to Arnesen on Apr. 3, 1979 entitled THERMO-VACUUM STRUCTURE, describes a building construction component that draws a partial vacuum from between a double layer of fabric. In this case, however, the partial vacuum is intended to act as a thermal barrier. In the process, however, the pressure differential supports the inner fabric layer and stresses the outer fabric layer in such a manner as to cause it to cling to a rigid form positioned between the layers.
U.S. Pat. No. 4,183,378 issued to Decker on Jan. 15, 1980 entitled LIGHT WEIGHT VACUUM MAINTAINED STRUCTURES, describes a light weight vacuum maintained structure intended for use in conjunction with an air ship or the like. The complex structure described includes an array of pressurized keystone shaped cells that cylindrically surround the interior of the structure within which a vacuum is drawn.
U.S. Pat. No. 5,579,609 issued to Sallee on Dec. 3, 1996 entitled RIGIDIZABLE INFLATABLE STRUCTURE, describes another version of a rigidizable dome-shaped inflatable structure that incorporates bundles of reinforcing fibers commingled with binder materials. The structure, after inflation, is rigidized by applying heat from an incorporated heat source.
U.S. Pat. No. 5,421,128 issued to Sharpless et al. on Jun. 6, 1995 entitled CURVED, INFLATED, TUBULAR BEAM, describes a curved, inflatable tubular beam whose strength is supplemented by a braided fiber shell and an array of external axial fibers. The angle of the braid helps determine the curvature of the inflated structure.
U.S. Pat. No. 5,546,707 issued to Caruso on Aug. 20, 1996 entitled POLYETHELENE INFLATABLE TUBE CONSTRUCTION DEVICE, describes an inflatable tube system incorporating discrete inflatable tube segments having terminal ends and a variety of mechanisms for the attachment of one segment to the other. A fabric covering of woven polyethylene material encloses the bladder to provide strength. Inflation air valves are positioned on end closures for the air bladder.
As indicated above, efforts to provide improved rigidity for air inflated structural components have focused primarily on external additions to the tubular air chambers that serve to strengthen the walls. Such external additions permit higher pressures (and thus greater rigidity) and directly add rigidity to the structural member once inflated. Unfortunately, all of these external additions to improve the structural integrity of the inflatable air beam add weight, complexity and expense to the portable buildings and enclosures constructed from these components. In addition, the move to higher pressures has resulted in an increased likelihood of explosive decompression as a result of fabric failure. Such unsafe ruptures continue to occur despite efforts to reinforce the outer shell of the tubular air chambers.
It would be desirable to have an air beam component that retained all of the benefits of typical air beam elements and added a rigidizing component to the air beam without greatly increasing the size, weight, complexity or cost of the air beam. It would be desirable if such a rigidizing component in an air beam could be easily implemented in conjunction with the inflation process and did not reduce the portability of the inflatable structure by decreasing the flexibility of the structure in an uninflated state. In other words, it would be desirable to have a rigidizing element that could alternately be made flexible or rigid depending upon the establishment or the removal of the structure.
It is therefore an object of the present invention to provide an air beam component that retains the benefits of typical light-weight air beam elements and adds a means for making the air beam rigid without greatly increasing the size, weight, complexity or cost of the air beam.
It is a further object of the present invention to provide a rigidizing component in an air beam element that is flexible prior to inflation of the air beam and becomes rigid subsequent to inflation.
It is a further object of the present invention to provide an air beam element with an incorporated rigidizing component that does not reduce the portability of an inflatable structure comprised of such air beam elements by decreasing the flexibility of the structure in an uninflated state.
It is the further object of the present invention to provide an improved hybrid air beam component comprising air pressure compartments and rigidizing components that eliminate the need for high pressure inflation and the resultant risk of explosive decompression.
In fulfillment of these and other objectives the present invention provides an air beam structure having reduced weight, increased rigidity, and lower inflation pressure requirements. The improved structure comprises a tubular cylindrical shell constructed from an air impermeable fabric closed at each end and having at least one inflation valve port. Fixed within the tubular cylindrical shell is a hollow xe2x80x9cIxe2x80x9d beam envelope comprised of a number of flexible, air impermeable walls that are sealed to the interior surface of the cylindrical shell. The hollow xe2x80x9cIxe2x80x9d beam envelope extends the length of the cylindrical tube and thereby defines at least four air chambers that are in air flow communication with the inflation valve port. The hollow xe2x80x9cIxe2x80x9d beam envelope likewise defines an interior longitudinal volume having an xe2x80x9cIxe2x80x9d shaped cross section that is isolated from the inflation air chambers. A quantity of micro bead particles or similar material is dispersed throughout the interior of the hollow xe2x80x9cIxe2x80x9d beam envelope which, when subjected to the compressive forces brought about by the pressurization of the air chambers, becomes rigidized in the two parallel and one orthogonal planes associated with the xe2x80x9cIxe2x80x9d beam cross section. The micro bead filled envelope is either vented to atmospheric pressure or connected to a vacuum source for establishing a differential pressure between the inside of the envelope and the air chambers exterior to the envelope. The improved air beam structure is utilized in groups or arrays that may be connected one to the other by fabric or sheet like materials to form a closed wall or roof type structure upon inflation. The method of use comprises inflating the air chambers within the air beam to establish the shape and size of the enclosure and then optionally subjecting the micro bead filled envelope to a vacuum source so as to create a pressure differential sufficient to compress and rigidize the micro beads enclosed therein.